The liquid crystal display panel is the main stream flat panel display device technology in the present market. All display devices need backlight to be the light source. The traditional backlight module comprises a backlight source having LEDs and a light guide plate. In a general side light type backlight module structure, the light guide plate of PET or PMMA plastic material uniformly mixes the side light and illuminates the same upward. After passing through the optical films, such as the diffuser and the prism, the light enters the liquid crystal display panel. Meanwhile, polarizers are adhered at positions of the incident light and the illuminating light at the upper, lower surfaces of the glass substrate to make the incident light be linearly polarized light. The polarization direction is changed with the liquid crystal for realizing the control of the illuminating light brightness. However, with such structure that a plurality of layers of optical films and the backlight module structure components exist, it is very difficult to make the display device have the ultra thin structure in thickness.